In the past, rotor and stator colloidal dispersion mills have been used for mechanically disintegrating components of, e.g., waste water sludge, paint, ink and the like to produce liquid suspensions with finely divided components. (See, for instance, U.S. Pat. Nos. 2,628,081, 2,706,621 and 5,240,599). In these patents, liquid containing immiscible liquid(s) and/or partially dispersed solid particulate component(s), are propelled by a rotor against the interior surface of a concentric stator ring having a plurality of radial passageways or slots intermittently spaced around its circumference. The slots have a constant, relatively narrow width compared to the circumference of the stator. The rotor is typically propelled at a very high velocity, e.g., usually between 5,000 to 12,000 feet per minute. As a result, the fluid and entrained immiscibles to be processed are subjected to strong centrifugal forces which induce an outward flow through the narrow slots of the stator.
In U.S. Pat. No. 5,240,599, the rotor itself has a peripheral ring with slots passing radially therethrough and fluid flow is primarily attributable to centrifugal force. When the rotor and stator slots come into alignment, the fluid is ejected from the rotor slots into the stator slots. All components carried in the ejected fluid have an initial resultant velocity attributable to the radial and tangential velocity imparted by the rotor. Predominantly tangential motion causes some portion of the immiscibles carried in the flow through the rotor slot to impinge on the interior radial surface of the stator slot emanating from the trailing edge of the slot, fracturing them into smaller sub-parts. This action is applicable to particles or to globules of undissolved fluids which can be broken down by impinging them against the stator slot walls.
Analysis of the flow exiting the rotor slots in the invention described in U.S. Pat. No. 5,240,599 reveals that the flow exits the rotor slot at approximately 1.degree. to 5.degree. above the tangent at the rotor slot tip. At this angle, impingement of the flow against the radial stator slot face occurs only for the instant when the rotor slot begins to discharge into the stator slot. The majority of the flow impacts the inner circumferential face of the stator at an angle of about 1.degree. to 5.degree.. Because the optimum angle of particle impact against the trailing stator slot face is 90.degree., a 1.degree. to 5.degree. tangential impact angle greatly reduces impingement efficiency. Because of this, mill efficiency is low (i.e., on the order of 3 to 4%) based on the number of passes through the rotor and stator head that most immiscible materials require before reaching their ultimate particle size.
In addition to the fluid discharge angle from the rotor slot, the clearance between the rotor and stator faces has been determined to be an important factor controlling the geometry of the impact dynamics. For example, 0.000097 seconds is required for the rotor slot to traverse the stator slot in a wastewater version of the dispersion mill as described in U.S. Pat. No. 5,240,599 running at an operational speed of 9,000 feet per minute. In that time, the fluid leaving the rotor slot travels 0.0098 inch towards the stator, which is roughly half the distance across the clearance gap of 0.017 inches. As a result, most of the immiscibles do not impact the trailing face of the radial stator slot, but instead impinge on the stator past the trailing edge of the stator slot.
One important application for apparatus to produce suspensions of finely divided matter is in the biological sciences, i.e., for breaking open or lysing cells, e.g., bacterial cells. Workers in the field of cell disruption have shown that pressures on the order of 5,000 to 20,000 psia are necessary to rupture bacterial cell membranes. Typical lysing processes rely on brute-force techniques to generate high pressures. For example, hydraulic cylinders raise the pressure of a flow stream up to the required pressure of 5,000 to 20,000 psia. The liquid is then forced through an orifice, split into two streams which are brought back together, and made to impinge against one another. This technique is far more energy intensive than comparable lysing with a dispersion mill, which produces these high pressures for a brief instant with each impact.
In summary, current rotor and stator designs for dispersing, disintegrating and comminuting immiscibles in a liquid provide less than optimal impingement angles, insufficient time for clearance gap traversal and insufficient pressure for cell lysing.